One problem in feeding a top sheet of media from a stack of sheets of media is that at least the next adjacent sheet may be fed at the same time. Accordingly, various separating means have previously been suggested for separating a top sheet of a stack of sheets of media from the next adjacent sheet when the feed is from the top of the stack of sheets of media.
It is known to separate a top sheet of a stack of sheets from the next adjacent sheet through using a dam, which is an element having an inclined surface in the path of the top sheet as it is fed from the stack of sheets so that its leading edge will strike the inclined surface of the element. In a printer, for example, the advancement of more than one sheet from the stack of sheets can cause jamming. Therefore, it is necessary to avoid simultaneous advancement of more than one sheet from a stack of sheets of media to a processing station such as a printer, for example.
One previously suggested dam has its inclined surface formed with longitudinally extending ribs so that there is corrugation of a sheet of media between the substantially parallel ribs when the sheet is advanced longitudinally along the exterior surface of each of the ribs. This corrugation is due to a buckling force created by resistance to movement of the sheet by the exterior surface of each of the ribs. While this dam is usually successful in separating an uppermost or top sheet from the next adjacent sheet in a stack of sheets, it is not always successful. Thus, multiple feeding of sheets can occur as the sheets advance up the inclined, ribbed surface of the dam.
Additionally, a surface having a coefficient of friction low enough to separate a relatively heavy media such as cardstock, envelopes, and labels, for example, without causing the feed motor to have too heavy a load will result in more multiple sheet feeding of a relatively light weight media with high friction between sheets such as bond or xerographic paper, for example. This presents the problem of whether to have an inclined surface of a dam capable of reliably separating heavy media or light media. This is not desirable with a printer since a printer needs to be capable of printing both heavy and light media to have a sufficient market.